One common type of earplug includes a cylinder punched out of a plate of elastomeric polymer foam material, or a bullet-shaped member molded of such polymer foam material. It is difficult to insert the front portion of an ordinary foam earplug into the ear canal, because the rear end of such earplug collapses as it is pushed forward in an attempt to insert the front portion into the ear canal. As a result, such earplugs of foam are commonly formed of slow recovery material which can be rolled between the fingers to a small diameter and inserted into the ear canal and held therein while the front end of the earplug expands during a period of perhaps 30 seconds. If a worker""s hands are dirty, then the rolled earplug will pick up dirt, which is a disadvantage of such earplugs.
Another type of earplug, such as shown in U.S. Pat. Nos. 4,434, 792 and 5,573,015, includes a body of resilient foam or very soft solid rubber molded with an axial passage, and a stiffening rod of more rigid material lying in the passage. The stiffening rod resists column-like collapse, and pushes the front end of the body into the ear canal. The stiffening rod has a disadvantage in that it makes the front end of the body stiffer against radial compression so greater force is required to insert the body front end into the ear canal and the earplug is not as comfortable. An earplug that could be constructed at low cost, which could be installed in the ear canal without requiring rolling between the fingers, and which had a front body portion that was easily radially compressed for easy of installation and comfort, would be of value.
Many earplugs are constructed in pairs that are connected by a cord. Such cords are commonly attached to an earplug by forcing an end of a cord into the earplug, with adhesive on the cord end bonded to the earplug. If the earplug is of soft foam, such insertion may be difficult. In practice, the cord is often inserted off center from the earplug axis and sometimes comes out when pulled to take out the earplug. It would be desirable if an earplug were constructed that facilitated reliable and accurately on-axis installation of a cord end in the earplug.
In accordance with one embodiment of the present invention, an earplug is provided with a body front portion that can be inserted into the ear canal to seal thereagainst, and a stiffener that preferably lies within the body front portion to stiffen the earplug against column-like collapse, wherein the stiffener is easily radially compressed. The stiffener is in the form of a tube, which provides high resistance to column-type collapse, but which can be easily radially compressed. The body of soft elastomeric material is molded and the tubular stiffener may be molded integrally with the body. In most cases, the body is formed of a soft foam material and the inside of the tubular stiffener is filled with soft foam material. Simultaneous molding of the body and material within the tubular stiffener, is facilitated by forming the stiffener with a slot extending parallel to its length, so material can pass from around the tubular stiffener and through the slot to fill the inside of the tubular stiffener with the same foam material that forms the body of the earplug.
Earplugs of the above type can be molded by extrusion of foamable material through a die head. The tubular stiffener can be passed through the middle of the die head opening, to result in an elongated extrusion comprising a tubular stiffener surrounded by soft foam material that is bonded around the outside of the stiffener. The elongated extrusion can be partially separated into individual earplugs by compressing and cutting the foamable material of the body prior to complete foaming and setting, resulting in a chain of connected earplugs. The chain can be stored and later cut into individual earplugs as needed, or the chain can be immediately cut into individual earplugs such as at the time when the foam material is compressed to separate foam material of sequential earplugs.
The tubular stiffener lying within soft elastomeric material, facilitates the production of specialized earplug pairs that are connected together by a cord. Such cord can be inserted into the tubular stiffener of each earplug of the pair and fixed in place as by adhesive. The fact that the stiffener provides a passage accurately centered on the axis of the earplug, results in the cord ends being more easily and reliably inserted into the earplug and lying more accurately on the axis of the earplug.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.